The broad objectives of the proposed research are to study the mechanisms and factors involved in the ability of the heart to regulate coronary blood flow and ventricular function from a physiological and mathematical point of view in a cooperative manner. This requires synergistic physiological and mathematical model development so that the physiological interferences are minimized and mathematical complications reduced. To this end a paced isolated heart perfused with a modified Krebs-Hensleit solution will be used. All pertinent mass transport and left ventricular variables will be recorded including perfusion pressure, coronary flow, arterial and venous PO2, tissue PO2 (Whalen PO2 microelectrode), left ventricular pressure and corresponding time derivative. A mathematical mass transport model will be developed and constrained to duplicate the measured PO2 histograms and whole organ closed loop gains. Additional physiological measurements will be made and modeling assumptions relaxed to aid model verification and demonstrate the models adequacy (or inadequacy). These models should suggest critical physiological experiments that could provide definitive data concerning (a) the possible mechanisms of coronary blood flow regulation and (b) the mass transport factors involved in the modulation of myocardial O2 consumption and/or ventricular function. These models should clarify interpretation of PO2 histograms and might suggest clinically useful measures of tissue level phenomena.